An antiquated, turn-of-the-century steel awning on a Bronx building saved the life of a toddler who plummeted 30 feet after climbing over the guard on his fourth-floor window yesterday.

The 21/2-year-old boy, Albert Otero, landed on the corrugated steel overhang – which remains attached to the recently renovated former garment factory at 452 E. 148th St. because the building was designated a city landmark.

“If not for that awning, this kid is history,” said Hector Santana, the superintendent of a neighboring building, who was the first to reach Albert after his 9:30 a.m. tumble.

“He would have broken his neck on the cement. He’d be dead.”

As it is, Albert suffered a broken collarbone and head bruises from the three-story fall. He was taken to Lincoln Hospital in serious-but-stable condition.

He was later transferred to New York-Presbyterian Hospital in Washington Heights to undergo neurological testing.

Albert’s mother, Jacqueline Vasquez, her two other children and a tenant were asleep when the tot managed to raise the window nearly a foot above the window guard.

A next-door neighbor saw the fall.

“He looked like a twisted rag doll. He didn’t have on any clothes, just the diaper,” said Elsa Morales, 35.

The window was pushed all the way up, leaving a gap measured by a city Health Department inspector at 11 inches, meaning the guards weren’t properly installed, a department source said.

Department rules state that the gap between the bottom of an open window and the top of the window guard can be no more than 4½ inches.

A spokesman for the building’s owner, L&M Hub Associates, said the company would not comment until it completed its own investigation.